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Worksheet: Redshift

In this worksheet, we will practice calculating the radial velocity of a star or galaxy using the amount by which absorption lines in the spectrum of light from it are shifted.

Q1:

The diagram shows the spectral lines in the light from two galaxies, as well as the same spectral lines in the light from a laboratory source.

How is Galaxy A moving relative to Earth?

AIt is stationary relative to Earth.

BIt is moving toward Earth.

CIt is moving away from Earth.

How is Galaxy B moving relative to Earth?

AIt is moving away from Earth.

BIt is stationary relative to Earth.

CIt is moving toward Earth.

Which galaxy is moving faster relative to Earth?

AGalaxy A

BGalaxy B

Q2:

An astronomer looks at the spectrum of light coming from a distant star. He notices that
the spectral lines in the spectrum have been shifted toward the blue end of the spectrum. Is
the star moving toward or away from the astronomer?

AThe star is moving toward the astronomer.

BThe star is moving away from the astronomer.

Q3:

An astronomer looks at the absorption lines in the spectrum of light coming from a distant
galaxy. He identifies the absorption lines of hydrogen, which makes up most of the galaxy.
He then compares these lines to the same absorption lines from a laboratory sample. His
results are shown in the diagram.

How is the galaxy moving in relation to Earth?

AIt is stationary relative to Earth.

BIt is moving toward Earth.

CIt is moving away from Earth.

Q4:

The galaxy NGC 4945 is approximately 11.7 million light-years away from Earth and is moving away from it at a speed of 563 km/s. By how much is the 656 nm absorption line of hydrogen redshifted by this relative motion? Use a value of 3×10/8ms for the speed of light. Give your answer in nanometers to 3 significant figures.

Q5:

The light received from very distant galaxies is shifted toward the red end of the spectrum. How are these galaxies moving in relation to Earth?

AThey are stationary in relation to Earth.

BThey are moving toward Earth.

CThey are moving away from Earth.

Q6:

If a star or galaxy is moving very fast away from Earth, the wavelengths of the light
received from it will be , making the star or galaxy appear .

Adecreased, redder

Bincreased, bluer

Cdecreased, bluer

Dincreased, redder

Eincreased, brighter

Q7:

The Andromeda galaxy is one of the galaxies closest to the Milky Way and has been observed
to be moving toward it at a speed of 300 km/s. Light coming from Andromeda is therefore
blueshifted. If light received at Earth from Andromeda has a frequency of
6.20×1014 Hz, what was the frequency of the light
when it was emitted from Andromeda? Use a value of 3×108 m/s for the speed of
light.

A16.5×1014 Hz

B25×1014 Hz

C95.4×1014 Hz

D6.19×1014 Hz

E61×1014 Hz

Q8:

An astronomer on Earth looks at the light coming from a distant galaxy.
He sees that the
486 nm absorption
line for hydrogen has been redshifted by
20 nm.
How fast is the galaxy moving away from Earth?
Use a value of
3×108 m/s
for the speed of light.
Give your answer in scientific notation to
3 significant figures.

A123×107 m/s

B12.3×107 m/s

C6.39×107 m/s

D1.23×107 m/s

E744×107 m/s

Q9:

The diagram shows some of the absorption lines for hydrogen in the electromagnetic spectrum. If a galaxy is moving away from Earth at a speed of 1.9×104 km/s, by how much would the absorption line with the shortest wavelength be redshifted? Use a value of 3×108 m/s for the speed of light. Give your answer to the nearest nanometer.

Q10:

If a star or galaxy is moving very fast toward Earth, the wavelengths of light received from it will be , making the star or galaxy appear .

Aincreased, bluer

Bdecreased, redder

Cincreased, redder

Ddecreased, bluer

Edecreased, dimmer

Q11:

An absorption line normally at 552 nm appears at 585 nm in the spectrum of light coming from a galaxy. How fast is the galaxy moving away from Earth? Give your answer in kilometers per second and in scientific notation to 3 significant figures.

A7.99×104 km/s

B65.3×104 km/s

C99×104 km/s

D1.79×104 km/s

E4.2×104 km/s

Q12:

The diagram shows the visible part of the electromagnetic spectrum. Some of the absorption
lines of hydrogen are shown on the spectrum.

What is the wavelength of the absorption line that has the shortest wavelength?

What is the wavelength of the absorption line that has the longest wavelength?

What is the wavelength of the absorption line that has the highest frequency?

What is the wavelength of the absorption line that appears in the red part of the
spectrum?

Q13:

The light emitted from two galaxies, A and B, is observed and the spectral lines in each
are shifted toward the red end of the spectrum. Galaxy A is observed to have a greater
redshift than Galaxy B. Which galaxy is moving faster away from Earth?

AGalaxy A

BGalaxy B

Q14:

A very distant galaxy is moving away from Earth at a speed of 1.8×10/4kms. Hydrogen within the galaxy absorbs light that has a wavelength of 410 nm, creating an absorption line in the spectrum of light from the galaxy. At what wavelength of light does this absorption line appear when the light reaches Earth? Use a value of 3×10/8ms for the speed of light, and give your answer to the nearest nanometer.

Q15:

Light with a frequency of 4.6×1014 Hz is emitted from a galaxy. When
it is received at Earth, the frequency of the light has been reduced by
2.0×1013 Hz. How fast is the galaxy receding
away from Earth? Use a value of 3×108 m/s for the speed of light. Give your answer in
kilometers per second and use scientific
notation to 2 significant figures.

A1.3×106 km/s

B89×104 km/s

C78×104 km/s

D1.3×104 km/s

E13×104 km/s

Q16:

The diagram shows the absorption lines in a spectrum from a distant star compared to those
in a spectrum from a laboratory sample. How is the star moving relative to Earth?